There are many different types of adjustable stairways presently available For example, there is the familiar steel parallelogram configuration having four spaced stringers adjustably supporting the steps. This type is frequently used as a temporary stairway for a building or home. Adjustable stairways are also common on docks which undergo a rising-and-falling motion due to the change of tide. In all of these adjustable stairways, the stringers or side supports of the stairs are spaced in a parallelogram-type configuration with the pair of stringers on each side which support the steps spaced from each other. While this construction does provide an adjustable stairway, the resultant structure is inherently weak since the strength of the stairway is only as good as the strength of any one of the elongated stringers making up the sides.